TST: Test for #9764 fix

Author: tomazberisa

pandas/tests/test_format.py

@@ -2986,6 +2986,20 @@ def test_format(self):
         self.assertEqual(result[0], " 12")
         self.assertEqual(result[1], "  0")
 
+    def test_output_significant_digits(self):
+        # relevant to issue #9764
+        d=pd.DataFrame({'col1':[9.999e-8, 1e-7, 1.0001e-7, 2e-7, 4.999e-7, 5e-7, 5.0001e-7, 6e-7, 9.999e-7, 1e-6, 1.0001e-6, 2e-6, 4.999e-6, 5e-6, 5.0001e-6, 6e-6]})
+        
+        expected_output={
+            (0,6):'           col1\n0  9.999000e-08\n1  1.000000e-07\n2  1.000100e-07\n3  2.000000e-07\n4  4.999000e-07\n5  5.000000e-07',
+            (1,6):'           col1\n1  1.000000e-07\n2  1.000100e-07\n3  2.000000e-07\n4  4.999000e-07\n5  5.000000e-07',
+            (1,8):'           col1\n1  1.000000e-07\n2  1.000100e-07\n3  2.000000e-07\n4  4.999000e-07\n5  5.000000e-07\n6  5.000100e-07\n7  6.000000e-07',
+            (8,16):'            col1\n8   9.999000e-07\n9   1.000000e-06\n10  1.000100e-06\n11  2.000000e-06\n12  4.999000e-06\n13  5.000000e-06\n14  5.000100e-06\n15  6.000000e-06',
+            (9,16):'        col1\n9   0.000001\n10  0.000001\n11  0.000002\n12  0.000005\n13  0.000005\n14  0.000005\n15  0.000006'
+        }
+
+        for k, v in expected_output.items():
+            self.assertEqual(d[k[0]:k[1]].__str__(), v)
 
 class TestRepr_timedelta64(tm.TestCase):